1. Field of the Invention
The present invention relates to a communication apparatus which shares a single line with another communication apparatus and performs a communication operation in accordance with a remote command from the another communication apparatus.
2. Related Background Art
A facsimile apparatus which shares a single telephone line with a telephone set and performs a facsimile Communication in accordance with a remote command from the telephone set has been known in the art. Such a facsimile apparatus is installed remotely from the telephone set and is connected through a network control unit (NCU). A user responds to a call signal from the line, and if the calling station is a facsimile terminal, the user manipulates a hook switch of the telephone set or a dialing ten-key to switch the line from the telephone set to the facsimile apparatus so that the facsimile reception is carried out (remote reception).
The NCU of the facsimile apparatus is configured as shown in FIG. 4.
In FIG. 4, a telephone line is connected to terminals L1 and L2, and a telephone set is connected to terminals T1 and T2. Numeral 1 denotes a CML relay which switches the telephone line between the telephone set and a modem. In a non-communication status, the CML relay 1 is connected to a so that the line is connected to the telephone set.
When a remote reception is to be carried out, a user depresses a hook switch of the telephone set for hooking to temporarily (usually less than one second) open the line. When the user does the hooking, a control unit of the facsimile apparatus detects the hooking by a current sensor 2 and switches the CML relay 1 to the modem (b) to carry out the communication.
Another configuration is shown in FIG. 5. In FIG. 5, when the user off hooks the telephone set in response to a call signal from the line and recognizes the calling station is a facsimile terminal, he/she manipulates the telephone set to dial a predetermined number (output a DTMF signal) in order to remotely receive the facsimile communication. The DTMF signal is sent from the terminals T1 and T2 to a terminal A through a transformer 8. A DTMF receiver is connected to the terminal A and the control unit recognizes the number outputted by the telephone set based on the output of the DTMF receiver. If it is the number for the remote reception, the control unit switches the CML relay 1 to b to carry out the communication. In this manner, the remote reception is attained.
However, in the switching by the hooking described above, the hooking is generated by the user by depressing the hook switch of the telephone set for a short period. Accordingly, depending on the duration of hooking, a switching unit may determine it as the opening of the line and disconnect the line, or the hooking of a given duration may be determined as the opening of the line or may not be determined depending on the switching unit. Thus, the remote reception is very unreliable.
Further, even if the remote reception normally operates, the user can hear nothing from the telephone set and cannot confirm whether the remote reception is successful or not.
Where the CML relay is switched by the DTMF signal, the DTMF detector may misoperate by a DTMF signal due to crosstalk on the line so that the CML relay may be switched during the speech communication to break off the speech.
Further, if the number for the remote reception is included in the number dialed by the user to call a destination, the CML relay is switched and the user cannot call. In order to solve the above problem, it has been proposed to limit the remote reception to a predetermined period after the reception of the call, but it is still not perfect because it does not permit the start of polling by the remote control and because of malfunction due to crosstalk from other lines.
The control of the facsimile apparatus by the remote telephone set is disclosed in U.S. patent application Ser. Nos. 372,622 (filed on Jun. 28, 1989); 453,364 (refiled on Dec. 20, 1989); 659,463 (refiled on Feb. 25, 1991); and 670,461 (refiled on Mar. 13, 1991).
However, no proposal to solve the above problems has been made.